A74 Transfer Switch; A56 Lower Front Panel Assembly; A60 And A61 Dc Bias Tees; A62 And A63 Directional Couplers - Agilent Technologies 8719ET Service Manual

8719ET/20ET/22ET Theory of Operation
8719ES/20ES/22ES Signal Separation: ES Models Only
RF Network Analyzers

A74 Transfer Switch

The output of the step attenuator is fed into the A74 transfer switch. This is a solid-state
switch. It switches between the PORT 1 and PORT 2 measurement paths, automatically
enabling alternate forward and reverse measurements. In addition, A74 provides an
internal termination for the measurement port that is inactive.

A56 Lower Front Panel Assembly

LEDs on the lower front panel indicate the status of the transfer switch.

A60 and A61 DC Bias Tees

The dc bias tees provide a means of biasing active devices with an external dc voltage
connected to the rear panel DC BIAS CONNECT ports. The dc voltage is applied directly
to the center conductor of the test port connectors. A blocking capacitor ensures that the
bias current goes only to the device under test, and not back into the source. Likewise, an
inductor in the bias path prevents RF from being imposed on the external dc supply.

A62 and A63 Directional Couplers

The test signal goes into the through-line arm of the couplers, and from there to the test
ports and the device under test (DUT). The coupled arm of the couplers carries the signal
reflected from or transmitted through the device under test to the receiver for
measurement. The coupling coefficient of the directional couplers is nominally 14 dB
from 840 MHz to 40.05 GHz and 40 dB at 50 MHz.
Service Guide 12- 21